application is the national phase under 35 U.S.C. xc2xa7371 of prior PCT International Application No. PCT/JP97/04802 which has an International filing date of Dec. 24, 1997 which designated the United States of America.
The present invention relates to a process for producing alkenyl-substituted aromatic hydrocarbons, in which an alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof is reacted with a conjugated diene using a catalyst, thereby causing alkenylation at the xcex1-position.
Alkenyl-substituted aromatic hydrocarbons are useful as intermediate materials of fine chemicals such as agricultural chemicals, drugs, and chemical products, and also useful as the intermediate materials for the production of naphthalene derivatives. It is well known that they can be obtained by reacting an alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof with a conjugated diene in the presence of a basic catalyst.
For example, the following are such known processes:
a process using an alloy of sodium metal and potassium metal as the catalyst (see JP-B 50-17975 and JP-B 51-8930);
a process using a catalyst in which sodium metal is carried on a support obtained from aluminum hydroxide and potassium hydroxide (see JP-A 6-293673);
a process using a catalyst composed of an aromatic compound that forms a charge-transfer complex with sodium metal and an alkaline earth metal salt (see JP-B 8-59523); and
a process in which a catalyst carrying an alkali metal on a support is filled in a reaction tube and production is achieved by flow-through reaction in a fixed-bed system (see U.S. Pat. No. 4,990,717).
The above catalysts and processes, however, have drawbacks that the rate of conversion of an alkyl-substituted aromatic hydrocarbon must be kept lower by reducing the amount of conjugated diene to be charged, relative to that of alkyl-substituted aromatic hydrocarbon, because of their low catalyst activity and insufficient selectivity.
The present inventors have extensively studied various alkenylation catalysts for the purpose of developing an excellent process for producing an alkenyl-substituted aromatic hydrocarbon by alkenylation at the xcex1-position of a side chain of an alkyl-substituted aromatic hydrocarbon. As a result, they have found that a catalyst obtained by the action of an alkali metal compound and an alkali metal or an alkali metal hydride on a metal oxide selected from alumina or hydrotalcite by heating in a specific temperature range can exhibit remarkably high activity on alkenylation and provide a desired alkenyl-substituted aromatic hydrocarbon with high efficiency, even if the catalyst is used in a small amount.
The present inventors also have extensively studied various alkenylation catalysts and their additives for the purpose of developing a further excellent producing process. As a result, they have found that when the reaction is carried out in the presence of an alkylaminopyridine using an alkali metal or an alloy thereof, or a catalyst carrying any of them on an inorganic compound support, or a solid base catalyst obtained by the action of an alkali metal compound and an alkali metal or an alkali metal hydride on a metal oxide selected from alumina, alkaline earth metal oxides, hydrotalcite, silica-alumina, or zeolite by heating in a temperature range of 70xc2x0 C. to 700xc2x0 C., higher selectivity in alkenylation can be attained with the catalyst activity being retained, and a desired alkenyl-substituted aromatic hydrocarbon can be produced with high efficiency, even if the catalyst is used in a small amount. After further various studies, they have completed the present invention.
Thus, the present invention provides:
1. a process for producing an alkenyl-substituted aromatic hydrocarbon by alkenylation of an alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof with a conjugated diene, characterized in that the process involves the use of a catalyst selected from:
(1) a solid base catalyst obtained by the action of potassium hydroxide directly on alumina by heating in a temperature range of 300xc2x0 C. to 600xc2x0 C. and the subsequent action of sodium metal or sodium hydride on the alumina by heating in the same temperature range;
(2) a solid base catalyst obtained by the action of an alkali metal compound on alumina by heating and the subsequent action of potassium metal or potassium hydride on the alumina in an atmosphere of an inert gas by heating, both in a temperature range of 70xc2x0 C. to 500xc2x0 C.; or
(3) a solid base catalyst obtained by the action of a potassium compound and sodium metal on hydrotalcite or by the action of a potassium compound and sodium hydride on hydrotalcite, both by heating in a temperature range of 100xc2x0 C. to 700xc2x0 C. in an atmosphere of an inert gas; and
2. a process for producing an alkenyl-substituted aromatic hydrocarbon by alkenylation of an alkyl-substituted aromatic hydrocarbon containing a hydrogen atom at the xcex1-position of a side chain thereof with a conjugated diene, characterized in that the process involves the reaction in the presence of an alkylaminopyridine of formula (1): 
wherein R1 is hydrogen or C1-C6 lower alkyl, and R2 is C1-C6 lower alkyl, using as a catalyst, Na metal, K metal, or an alloy thereof, or a catalyst carrying any of them on an inorganic compound support, or a catalyst obtained by the action of an alkali metal compound and an alkali metal or an alkali metal hydride on a metal oxide selected from alumina, alkaline earth metal oxides, hydrotalcite, silica-alumina, or zeolite by heating in a temperature range of 70xc2x0 C. to 700xc2x0 C.
The present invention will hereinafter be explained in detail.
First, the following will describe the first embodiment of the present invention, i.e., a process for producing an alkenyl-substituted aromatic hydrocarbon by alkenylation of an alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof with a conjugated diene, using a catalyst obtained by the action of an alkali metal compound and an alkali metal or an alkali metal hydroxide on an metal oxide selected from alumina or hydrotalcite by heating in a specific temperature range.
Examples of the alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof, which are usually used, may include monocyclic aromatic hydrocarbons and condensed polycyclic aromatic hydrocarbons. The side chain alkyl group may be combined together to form a ring.
Specific examples of the alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof are toluene, ethylbenzene, isopropylbenzene, n-propylbenzene, n-butylbenzene, secbutylbenzene, isobutylbenzene, xylene, cymene, diisopropylbenzene, methyl-naphthalene, tetrahydronaphthalene, and indane. Preferably used are toluene, xylene, and ethylbenzene.
Examples of the conjugated diene, which are usually used, may include those having about 4 to about 10 carbon atoms, and they may be either in straight chain form or in branched form.
Specific examples of the conjugated diene are 1,3-butadiene, 2-methyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. Preferably used are 1,3-butadiene and 2-methyl-1,3-butadiene.
Examples of the catalyst, which can be used in the alkenylation of the present invention, may include catalysts (solid base catalysts) obtained by the action of an alkali metal compound and an alkali metal, or by the action of an alkali metal compound and an alkali metal hydride on a metal oxide selected from alumina or hydrotalcite.
The following will describe the solid base catalyst.
Examples of the solid base catalyst may include:
(1) a solid base catalyst obtained by the action of potassium hydroxide directly on alumina by heating in a temperature range of 300xc2x0 C. to 600xc2x0 C. in the air or under an atmosphere of an inert gas and the subsequent action of sodium metal or sodium hydride on the alumina by heating in a temperature range of 305xc2x0 C. to 550xc2x0 C. under an atmosphere of an inert gas, wherein the amount of potassium hydroxide to be used is 5% to 50% by weight, relative to the alumina, and the amount of sodium metal to be used is 2% to 15% by weight;
(2) a solid base catalyst obtained by the action of an alkali metal compound on alumina by heating in a temperature range of 200xc2x0 C. to 500xc2x0 C. in the air or under an atmosphere of an inert gas and the subsequent action of potassium metal or potassium hydride on the alumina by heating in a temperature range of 70xc2x0 C. to 40xc2x0 C. in an atmosphere of an inert gas, wherein the amount of alkali metal compound to be used is 5% to 70% by weight, preferably 10% to 50% by weight, relative to the alumina, and the amount of potassium metal or potassium hydride to be used is 2% to 10% by weight, relative to the alumina; and
(3) a solid base catalyst obtained by the action of a potassium compound and sodium metal on hydrotalcite or by the action of a potassium compound and sodium hydride on hydrotalcite, both by heating in a temperature range of 100xc2x0 C. to 700xc2x0 C. in an atmosphere of an inert gas. Potassium compound may be reacted in a temperature range of 200xc2x0 C. to 600xc2x0 C.
Specific examples of the sodium compound are sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, and sodium alkoxide.
The amount of alkali metal compound to be used is usually in the range of 5% to 70%, relative to the support.
In usual cases, an alkali metal compound is preferably allowed to act directly on a support just as it is in powder or flake form; however, it may also be dissolved or suspended in water or an organic solvent, followed by the addition to a support and the action by heating at a prescribed temperature. These steps may be performed in the air, or if required, under an atmosphere of an inert gas.
Examples of the alkali metal, which are preferably used, may include sodium metal, potassium metal, and alloys of sodium and potassium. In this case, of a preferred combination of a potassium compound and sodium metal or sodium hydride, or a combination of a sodium compound and potassium metal or potassium hydride; particularly preferred is a combination of a potassium compound and sodium metal and sodium hydride.
The alkali metal or alkali metal hydride is preferably used under an atmosphere of an inert gas, examples of which are nitrogen gas, helium gas, and argon gas.
The amount of alkali metal or alkali metal hydroxide to be used is usually in the range of 2% to 20%, relative to the support.
In the preparation of such a solid base catalyst, the heating time may vary depending upon the selected conditions; however, the action time is in the range of 0.5 to 10 hours for alkali metal compounds or 0.1 to 5 hours for alkali metals or alkali metal hydrides.
Thus, the solid base catalyst can be obtained, which has good fluidity and good operability, as well as extremely excellent activity on the desired reaction.
The reaction temperature is usually in the range of about 0xc2x0 C. to about 200xc2x0 C., preferably about 50xc2x0 C. to about 180xc2x0 C. The reaction pressure is usually in the range of about atmospheric pressure to about 20 kg/cm2, preferably about atmospheric pressure to about 5 kg/cm2.
The mole ratio of conjugated diene to alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof is usually in the range of about 0.01 to about 1, preferably about 0.05 to about 0.8.
The amount of catalyst to be used in a batch system is usually about 0.01% to about 20% by weight, preferably about 0.1% to about 10% by weight, relative to the aromatic hydrocarbon used. The reaction time is usually in the range of about 0.1 to about 50 hours, preferably about 0.5 to about 25 hours.
The total rate of supply of an alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof plus a conjugated diene in the flow-through reaction is usually about 0.01 to about 100 hrxe2x88x921, preferably about 0.1 to about 20 hrxe2x88x921, in LHSV.
The following will describe the second embodiment of the present invention, i.e., a process for producing an alkenyl-substituted aromatic hydrocarbon by alkenylation of an alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof with a conjugated diene, characterized in that the reaction is carried out in the presence of an alkylaminopyridine of formula (1): 
wherein R1 is hydrogen or C1-C6 lower alkyl, and R1 is C1-C6 lower alkyl, using as a catalyst, Na metal, K metal, or an alloy thereof, or a catalyst carrying any of them on an inorganic compound support, or a catalyst obtained by the action of an alkali metal compound and an alkali metal or an alkali metal hydride on a metal oxide selected from alumina, alkaline earth metal oxides, hydrotalcite, silica-alumina, or zeolite by heating in a temperature range of 70xc2x0 C. to 700xc2x0 C.
The alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof and the conjugated diene, which are used in this embodiment, may include those which are the same as used in the above first embodiment.
In this embodiment, Na metal, K metal, or alloys thereof, can be used as the catalyst. Preferably used are alloys of sodium and potassium at a weight ratio of 1:1 to 10:1. The amount of such a catalyst to be used is usually in the range of 0.01% to 10% by weight, preferably 0.03% to 5% by weight, relative to the alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof.
Examples of the inorganic compound, which are preferably used for carrying Na metal, K metal, or an alloy thereof, may include potassium carbonate and metal oxides, particularly alumina, magnesium oxide, calcium oxide, hydrotalcite, zeolite, and potassium carbonate. The amount of Na metal, K metal, or an alloy thereof to be used is usually in the range of 1% to 20% by weight, preferably 2% to 12% by weight, relative to the support.
The catalyst carrying Na metal, K metal, or an alloy thereof on an inorganic compound support is obtained by the action of both by heating in a temperature range of a melting point thereof to 500xc2x0 C., preferably 100xc2x0 C. to 400xc2x0 C., under an atmosphere of an inert gas such as nitrogen gas.
In the second embodiment of the present invention, besides Na metal, K metal, alloys thereof, and catalysts carrying any of them on an inorganic compound support, as described above, there can also be used a catalyst which is obtained by the action of an alkali metal compound and an alkali metal or an alkali metal hydride on a metal oxide selected from alumina, alkaline earth metal oxides, hydrotalcite, silica-alumina, or zeolite in a temperature range of 70xc2x0 C. to 700xc2x0 C. Examples of the alkaline earth metal oxide, which are preferably used, may include magnesium oxide, calcium oxide, and barium oxide. With the use of such a catalyst in the presence of an alkylaminopyridine of formula (1) as depicted above, the alkenylation can be carried out.
In the alkylaminopyridine of formula (1), the C1-C6 lower alkyl, which is represented by R1 or R2, may include methyl, ethyl, propyl, butyl, pentyl, and hexyl.
Examples of the alkylaminopyridine of formula (1) are dimethylaminopyridine, diethylaminopyridine, dipropylaminopyridine, dibutylaminopyridine, methylethylaminopyridine, methylpropylaminopyridine, methylbutylaminopyridine, methylaminopyridine, ethylaminopyridine, propylaminopyridine, and butylaminopyridine. These may be used in form just as it is commercially available, or if necessary, purified by distillation, recrystallization, or dehydration.
The amount of alkylaminopyridine to be added is usually in the range of 0.001% to 1.0% by weight, preferably 0.01% to 0.3% by weight, relative to the alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof.
In the process of the present invention, the alkenylation can be carried out using a catalyst such as described above, either in a batch system or in a flow-through system with a fluidized or fixed bed.
The reaction temperature is usually in the range of about 0xc2x0 C. to about 200xc2x0 C., preferably about 50xc2x0 C. to about 180xc2x0 C. The reaction pressure is usually in the range of about atmospheric pressure to about 20 kg/cm2, preferably about atmospheric pressure to about 5 kg.cm2.
The mole ratio of conjugated diene to alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof is usually in the range of about 0.01 to about 1, preferably about 0.05 to about 0.8.
The amount of catalyst to be used in a batch system is usually about 0.01% to about 20% by weight, preferably about 0.1% to about 10% by weight, relative to the aromatic hydrocarbon used. The reaction time is usually in the range of about 0.1 to about 50 hours, preferably about 0.5 to about 25 hours.
The total rate of supply of an alkyl-substituted aromatic hydrocarbon having a hydrogen atom at the xcex1-position of a side chain thereof plus a conjugated diene in the flow-through reaction is usually about 0.01 to about 100 hrxe2x88x921, preferably about 0.1 to about 20 hrxe2x88x921, in LHSV.
Thus, the alkenyl-substituted aromatic hydrocarbon is produced. According to the present invention, the desired alkenyl-substituted aromatic hydrocarbons can be produced with extremely high efficiency, even if the catalyst is used in a small amount, and even under mild conditions.
In addition, the handling of a catalyst and the treatment after the reaction are quite easy, so that the present invention is also advantageous in this regard.